Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$73.92	12.260%	$82.9826	$82.98	$83.00	$83.00
Purchase #2	$119.29	13.113%	$134.9325	$134.93	$134.95	$134.90
Purchase #3	$191.68	13.380%	$217.3268	$217.33	$217.35	$217.30
Purchase #4	$39.60	7.362%	$42.5154	$42.52	$42.50	$42.50
Purchase #5	$129.52	11.833%	$144.8461	$144.85	$144.85	$144.80
Purchase #6	$97.91	13.705%	$111.3286	$111.33	$111.35	$111.30
Purchase #7	$62.27	11.251%	$69.276	$69.28	$69.30	$69.30
7 purchase totals =	$714.19		$803.2080	$803.22	$803.30	$803.10